Strong-field Breit-Wheeler pair production in short laser pulses: Relevance of spin effects

Production of electron-positron pairs in the collision of a high-energy photon with a high-intensity few-cycle laser pulse is studied. By utilizing the frameworks of laser-dressed spinor and scalar quantum electrodynamics, a comparison between the production of pairs of Dirac and Klein-Gordon particles is drawn. Positron energy spectra and angular distributions are presented for various laser parameters. We identify conditions under which predictions from Klein-Gordon theory either closely resemble or largely differ from those of the proper Dirac theory. In particular, we address the question to which extent the relevance of spin effects is influenced by the short duration of the laser pulse.

Figure 1

Spectral energy density (arb. units) of the ultrashort pulse with a shape function given by Eq. (3) with $N_{\mathrm{osc}}=2$ and $\chi =0$. The characteristic zeros at integer multiples of the basic frequency ${\omega }_b={\omega }_c/N_{\mathrm{osc}}$ (as indicated by the subticks) are caused by the window function ${\mathcal{X}}_{[0,2\pi ]}(\varphi )$.

Figure 2

Ratio between the rates for Dirac and KG for different numbers of absorbed photons as a function of the velocity $\beta$ of the particles.

Figure 3

Angularly integrated probabilities in units of $1/m$ as a function of $p_{+}/m$ for ${\omega }_c={\omega }_{\gamma }=1.006m$, $N_{\mathrm{osc}}=2$, and ${\xi }_{\max }=0.02$.

Figure 4

Fully differential probability in units of $1/m$ for $p_{+}=0.15m$, ${\omega }_c={\omega }_{\gamma }=1.006m$, $N_{\mathrm{osc}}=2$, and ${\xi }_{\max }=0.02$. The angles $\vartheta$ and $\phi$ describe the positron emission direction and are measured with respect to the laser propagation and polarization directions, respectively.

Figure 5

Same as Fig. 3 but for ${\omega }_{\gamma }=1.4m$, ${\omega }_c=0.7m$, and ${\xi }_{\max }=0.2$.

Figure 6

Same as Fig. 3 but for ${\omega }_{\gamma }=1.006m$, ${\omega }_c=0.503m$, and (a) ${\xi }_{\max }=0.001$, (b) ${\xi }_{\max }=0.1$.

Figure 7

Same as Fig. 4 but for ${\omega }_{\gamma }=1.006m$, ${\omega }_c=0.503m$, and ${\xi }_{\max }=0.1$.